Integrated optical circuits comprise a substrate on which the optical structures are applied or into which the optical structures are inserted. The possibility of being able to produce optical waveguides of low attenuation is, in particular, of decisive importance here. Starting from the basic structure of a waveguide, various assemblies such as, for instance, couplers, interferometers, frequency filters and the like can be produced.
For the production of waveguides which can conduct electromagnetic waves, the propagation of the field is to be limited to a direction which is predetermined in each case by the waveguide. For this purpose, the "insulating" of the field to be conducted from the outer environment is necessary.
In optical communications, dielectric insulation means, in particular, are employed. In the so-called core region of a waveguide, there is a material which has a higher index of refraction than the material surrounding the core, i.e. the so-called wall region. As a result, the guided electromagnetic field decreases substantially exponentially, without dissipation of energy in the direction towards the wall so that such a small field strength is present at the wall boundary that the attenuation of the field which takes place there is, as a practical matter, unimportant. This type of wave guidance is frequently used not only in glass fibers but also in integrated optical waveguides.
In connection with integrated optical waveguides, a wave guidance by height profiles is furthermore known in which the dispersion is limited by lateral narrowing of the core zone. Finally, for use in active optical components there is also known for wave guidance the recovery guidance method in which a region having a higher amplification than the surrounding of the wall is produced in the core region of the waveguide.